Synchronizer for oscillators



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SYNCHRONI ZER FOR OSCILLATORS Filed Jan. 1o. 1942 2 sheets-sheet 1 Z@ fJr/vrf//wN/z//v 0K 50K 500 RMU/mf MHSTER @msm/rw? Y v f TUBE aff/M701?mm1/ENC),

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SYNCHRONIZER FOR OSCILLATORS I Filed Jan. l0, 1942 2 Sheets-Sheet 2JVENTOR.

Patented Nov. 13, 1945 SYNCHRQNIZER FOR OSCILLATORS Richard L. Campbell,Maywood, N. J., assigner to Allen B. Du Mont Laboratories, Inc.,Passaic, N. J., a corporation of Delaware Application January 10, 1942,Serial No. 426,322

(Cl. Z50-36) 7 Claims.

With this invention a control tube for an oscillator is operatednormally at zero potential, and positive or negative correctivepotentials are generated and applied to said control tube dependent uponthe direction of frequency correction desired. Also the alternatingcurrent signals applied to the control device are balanced out in theoutput so that it is not necessary to resort to elaborate lterprecautions in order to prevent frequency modulation of the masteroscillator by either of the controlling signals.

In carrying out this invention, means are provided for comparing twowave forms and deriving from these wave forms a direct current controlvoltage, depending upon the relative phases between the voltages, andusing the produced direct current voltage to actuate a reactance tubefor the purpose of holding one of the wave forms in step with the other.The invention will be particularly described in connection with anembodiment thereof which is suitable for causing the 60cycle output of atelevision synchronizing generator to remain locked in to a 60cyclepower line circuit. With this invention there is a gain in stability sothat synchronizing generators can be reliably operated. It will beobvious that it has other uses.

Early methods of providing a lock-in to a power line are known. One ofthese is described in my Patent 2,209,507 in whicha single ended type ofdetector is used to provide a direct current control voltage for areactance tube.

By the present invention earlier disadvantages are overcome. Forexample, spurious reactions from changes in power supply voltage andtemperature stability, etc., are overcome or avoided.

This invention makes use of a pair of diodes which detect the outgoingsignals in a balanced manner, so that the central operating point forthe reactance tube I is that point at which the balanced detectordelivers zero output voltage and the balanced detector is arranged sothat a phase shift of the sawtooth wave with respect to the sine wave inone direction from this balanced point will deliver a net positivecontrol voltage, while a. phase shift in the other direction willdeliver a net negative control voltage. In this way th'e normaloperating point for the master oscillator is such that the detector isdelivering no voltage, and any hum modulation which would be deliveredby the detector is at a minimum at by the reactance tube l.

2 controls a blocking oscillator or other suitable this point, thusobtaining greatest freedom from frequency modulation of the masteroscillator.

The invention may be more clearly understood by reference to theaccompanying drawings, in which:

Fig. 1 is a schematic diagram showing the circuit of the balanced diodefor comparing two wave forms; and

Fig. 2 shows several wave forms illustrating the principles of operationof the invention.

In Fig. 1, the double diode 6H6` has one diode section so connected thatit will deliver a negative voltage to the output load circuit and theother diode section so connected that it will deliver a positivedetected voltage to the output load circuit. These two voltages arearranged to buck one another, so that the net voltage difference betweenthe two detected signals is delivered to the reactance tube l indicatedin'block form after suitable direct current filtering. The synchronizinggenerator 3 also shown in block form is connected to a master oscillator2 which generates a sine wave. The oscillating frequency of this masteroscillator 2 is controlled to some extent This master oscillator impulsegenerator in the usual way, which in turn goes through several stages offrequency division to generate a cycle sawtooth wave as indicated by theblock 4. It is therefore always a definite sub-multiple of the masteroscillator frequency.

By this invention a comparison of this 60cycle sawtooth wave is madewith a power line 60cycle sine wave, or some other suitable referencefrequency, and a control voltage is generated to be applied to thereactance tube l s0 that the frequency as Well as the phase of thegenerated sawtooth wave will be locked in and kept locked in withrespect to this 60cycle power line. 'I'h'e sawtooth wave is appliedthrough the condenser 6 to the grid 'l of the 6J5 tube, which' is abalanced phase inverter tube delivering a signal of one polarity fromits anode circuit through the condenser 9 to the diode plate I0 of thediode GHG and delivering a signal of approximately equal amplitude butof .opposite polarity from its cathode circuit through the condenser I lto the other diode plate I2. The variable resistors i3 and i4 are usedto balance or equalize the amplitudes of the sawtooth waves which areapplied to the diode plates I0 and I2. Additional cathode-loaded tubesmay be inserted when desired in order to balance the system more nearlyperfectly.

The load circuits in the cathodes I5 and I6 of the diode GHG are alsobalanced as indicated by the resistors I1 and I8, and the condensers I8,20 and 2l.

'I'he application of balanced sawtooth waves of opposite polarities tothe two diodes and the balanced load circuits in the cathodes of thediodes cause one sawtooth wave to generate a signal at the point 25which is opposed by the detected signal from the other sawtooth wave. Asine wave voltage suitably isolated by the 500,000 ohm resistors 26 and21 is inserted in a balanced manner in the double diode 6H6 so that thediode plates I and I2 are driven by avoltage wave form which is the sumof the sawtooth and the sine wave, and the wave forms at the diodeplates will chang their shapes and consequently their energy content inthe positive excursion portion of the cycles as the phase of thesawtooth shifts with respect to the phase of the sine wave.

This will be more clearly understood by reference to Fig. 2, in whichthe section A shows the sine wave form, and the three divisions ofsection A represent three columns, the first column showing theconditions where the sawtooth wave form has its rapid return occurringat the 180 phase point of the sine wave, the second column has thesawtooth wave rapid return occurring at the 270 phase point of the sinewave, and the third column has the rapid return of the sawtoothoccurring at the 360 phase point of the sine wave. The wave forms at Bshow the sawtooth waves applied from the lower cathode circuit of the6J5 tube to the plate I2. The amplitude ratio between the signals at Aand B may be adjusted by means of the variable resistors I3 and I4. Thewave forms at A are illustrative of the signals that are delivered bythe 60-cyc1e input 30 and the transformer 3i to the conductor 32 that isconnected between the resistors 26 and 21 at one end and the resistorsI1 and I8 at the other end.

Both the wave forms A (Fig. 2) and the wave forms B represent thesignals before mixing has taken place. The circuits are so arranged thatthe voltages are added in the respective network, so that a summationvoltage is actually applied to the plate I0 and the plate I2 of thediode 6H6. On Fig. 2 the wave forms designated as A+B are the wave formswhich are applied to the diode plate I2 of the diode 6H6.

These wave forms represent the signals which are being applied to thediode before considering the conductance of the diode. The diode passescurrent, however, when the plates I0 and I2 become positive with respectto the cathodes I5 and I6. When the diode is passing current a furthernetwork of resistors I1 and I8 is shunted across these wave forms ofA+B, causing the positive excursions of the wave forms to be attenuatedor reduced in aplitude according to the newly applied lower impedance ofthe load circuit. In practice, this simply means that the energy contentof the positive excursion portion of the wave forms shown at A+B are thecontrolling factors in determining how much direct current voltage isgenerated in the detector circuit of the cathode load of tube 6J5.

The other diode plate I0 has a sawtooth wave form applied to it from theupper or plate circuit of the 6J5 tube, which is represented by thediagrams at C of Fig. 2, which, by mixing with the wave forms A in thethree phases mentioned. result in the three wave forms shown at A14-.Cin Fig. 2.

The diode plate I2 has its cathode I6` grounded, and therefore developsits detected signal essentially as a plate output diode, the rectifiedvoltage appearing across the resistor 21 through the transformersecondary 3| and across the resistor I8 to ground. When the plate I2 ofthe diode 6H6 draws current with respect to the cathode Ii, this platestores a charge in the condenser 20 so that the point 30 becomesnegative with respect to ground, thus preventing momentarily any furtherflow of current in this diode. When the wave form of A+B again returnsto its negative portion this condenser 20 will hold a negative chargefor a time, thus giving the normal detector action. On the other hand,the diode IIJ-I5 is connected with part of its effective load circuit inthe plate III network and part of the effective load circuit in itscathode I5 network, so that when the plate IIl starts to conduct, thecathode I5 will become positive with respect to the point 30, developinga voltage across the resistor I1 which is retained by the action of thecondenser I9. The resistors I1 and I8 are connected in series, so thatthese opposing voltages are added to one another, and whichever voltageis the larger will determine the net voltage delivered to the connection25 and on through the filtering stages 26 to the reactance tube I.

Therefore the diode I2-I6 as connected tends to deliver a negativesignal derived from the wave forms A+B to the point 30, and thence tothe reactance tube I. The diode III-I5 tends to deliver a positivesignal derived from the wave forms A+C to the point 30, and thence tothe reactance tube I. By a comparison of the wave forms A+B at the threephase relations plotted with the wave forms A+C at the correspondingphase positions, it can be seen that the positive energy in the waveform designated byreference character 40 (Fig. 2, A+B) is approximatelythe same as the positive energy shown in the crosshatched region of thewave form designated by reference character 5I. The reversal in shape ofthe wave forms is not serious, since the diode detectors have a lowfrequency detecting filter in their cathode circuits and. the outputload responds essentially to the energy in these wave forms. But theWave form of reference character 4I contains more energy in its positiveexcursion than the wave form 40, and the wave form 50 at this same phaserelation contains less energy than the ywave form 5I. Since wave form 4Idelivers a negative detected signal and wave form 5II delivers apositive detected signal, it can be seen that at the phase relation ofthe negative detected signall will predominate in magnitude, and a netnegative voltage will be delivered to the terminal 30 (Fig. l). Thisnegative voltage, applied to the reactance tube I, tends to slow downthe master oscillator 2, causing the sawtooth wave to tend to shift backtoward the 270 phase point.

On the other hand, if the master oscillator 2 is running too slowly, thephase relation of the sawtoothv with respect to the sine wave may be, asillustrated (right hand end of Fig. 2, A and C) at 360. In this case theenergy in the positive cross-hatched portion oi 52 is seen to be largerthan the energy in the positive cross-hatched portion of 42, and thediode I0-I 5, to which the wave form of A+C is fed, will deliverpositive control signal which predominates in magnitude and thusincreases the master oscillator frequency momentarily, causing the phaseof the sawtooth Wave to shift back toward the 270 point to anintermediate phase angle which is the position of equilibrium.

If the master oscillator 2 is on the correct frequency which can bedetermined by closing the switch 33, then opening the switch 33 willconnect the balanced detector control circuit and the sawtooth wave willbeat against the sine wave thus generating a control voltage which willshift the master oscillator frequency until the phase relation is at thelow stable point. This point corresponds to the 270 diagram, Fig. 2,where it can be seen at once that the positive cross-hatched energy ofwave form 40 (Fig. 2, A+B) is equivalent to the positive cross-hatchedenergy of wave form I (Fig. 2, A+C), and therefore the output netvoltage will be neither positive nor negative and will be balanced forcontrol voltage, and furthermore will be balanced for any surge voltagesfrom power supplies or from other voltages which might otherwise get onthrough the integrating filter.

There will be another condition in which .the wave form of A+B (Fig. 2)in its positive portion will have the same energy as the wave form A-l-Cin its positive portion, but this other condition is at a phase relationsuch that the detected voltage will tend to throw the frequency fartheroi the correct value rather than toward its correct value. With thiscircuit it is found that the master oscillator may be held in step overa phase relation from 180 to 360 of the sine wave.

This is adequate for many applications, but in some cases it may bedesirable to lcause the 60- cycle sine wave from the power line tocontrol directly a sawtooth wave form and then utilize the same balanceddetector circuit to compare the power line sawtooth with thesynchronizing generator sawtooth, thus making it possible to iind astable control point for phase angles essentially anywhere within the360, as can be done with this invention.

The principles of this balanced detector circuit can be used forcomparing other types of wave forms with one another for controlpurposes, such as locking-in the switch oscillators of a televisionreceiver with respect to incoming synchronizing pulses or forcontrolling the oscillator of a frequency modulated transmitter withreference to a crystal oscillator.

While specific values are shown on the circuit diagram, it is wellunderstood that the principles of operation of the circuit are notconfined to any speciflc input signal amplitudes, and the values of thecircuit components may be changed very widely and still yieldsatisfactory performance.

What is claimed is:

1. A synchronizer for an oscillator, comprising two diodes, means for.applying impulses in phase opposition from said oscillator to the anodesof said diodes, and means to apply low frequency since wave impulses inparallel between the plates and cathodes of said diodes, one of saidcathodes being connected to -ground and the other one to saidoscillator.

2. The device of claim l, in which resistors are connected in seriesbetween said anodes.

3. The device of claim 1, in which resistors are connected in seriesbetween said cathodes.

4. The device of claim 1, in which two resistors are connected in seriesbetween the anodes of said diodes and two capacitors are connected inseries between the cathodes of said diodes.

5. The device of claim 1, in which two resistors are connected in seriesbetween the anodes of said diodes and two capacitors are connected inseries between the cathodes of said diodes and two resistors in seriesare connected in parallel with said capacitors.

. 6. The device of claim 1, in which a capacitor is connected betweensaid other one of said cath-4 odes and ground.

7. In a synchronizer for an oscillator, a balanced phase invertercomprising a vacuum tube having its grid connected to said oscillator,diodes having their plates connected respectively to opposite sides ofsaid inverter whereby signals from said oscillator are connected inphase opposition to said diodes, one of said diodes having its cathodegrounded, balanced load circuits connected to the cathodes of saiddiodes, means to apply a low frequency sine wave voltage in phase to theplates of said diodes, and a connection from said balanced load circuitsto saidoscillator whereby the frequency of said oscillator'iscontrolled.

RICHARD L. CAMPBEIL.

